Slam Help Please

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M

Mlamb

Well-known member
Oct 2, 2017
67
Sarasota/Fl
My sons pool was eating chlorine, so did a OCLT and from 8ppm at sundown dropped to 2ppm at sunrise. He started a slam and with a 70 cya set a 28ppm chlorine level and has been able to maintain that level with a lot of chlorine additions. For the past three days, the water has been very clear a 0cc’s. The slam has been going on for 4 days. Last night he overshot the chlorine by bringing it up to 36ppm, he tested twice to be sure, only to have it drop to 28ppm in the AM, still clear water and 0cc’s. He’s brushed and cleaned the filter daily and checked all the nooks and crannies. Not sure how to proceed…help please.
 
There are be some unusually FC drops when the FC goes well above the designed SLAM FC level. Since your son seemed to do just that, I would re-accomplish another OCLT. Be sure to not go over the FC of 28. In fact, just for the next test, even if it's slightly below 28 it may help to provide a more steady/reliable FC test for the OCLT. But if he looses more than 1 ppm, the SLAM should continue.
 
Tested water last night at 8pm and chlorine reading was 27. Tested this morning at 7am and reading was 26 and 0 cc and crystal clear water so passed the OCLT. Now from 7am to 2:30pm chlorine dropped to 15ppm. Is that excessive or expected? Weather is hot and sunny.
 
The higher the FC the faster the drop as the CYA only protects what it can and anything unprotected has a very short half life
 
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Shapshftr said:
I don't have a SWCG, but mine is currently at 60, which I'm slowly bringing down. But still have no problems with my water balance or clarity.
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Chlorine lock is a made up term, a myth. Many here run their pools 60-80. If you don't follow the FC/CYA and let your FC drop, you can get algae. It can be hard to slam when your CYA is above 60, but doable. 80 and above, better to drain a bit before SLAM. If you follow the FC/CYA recommended levels, you will not get algae.

Debunking the "Chlorine Lock" Myth

I stumbled onto a web page entitled Cyanuric Acid - Debunking the "Chlorine Lock" Myth that was information supplied by Bio-Lab. This is somewhat old as the page was last updated in 2003, but I wanted to comment on this since it is a perfect example of how scientific literature and experiments...
www.troublefreepool.com www.troublefreepool.com
 
Mlamb said:
So the drop from 26 to 15ppm over eight hours on a sunny hot day is not necessarily excessive?
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Nope.
Mlamb said:
As the chlorine drops to the high single digits the loss should slow down significantly?
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Yes, well significantly? On a hot sunny day I can lose 4-5.5FC in a day, when my FC is 9-10.
 
Shapshftr said:
FC and TC should be the same. If not, you have chlorine lock.
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This is not true. I have a cover and regularly have .5CC with the cover on. When I remove the cover for 1/2 hour my CC will go to zero.

“Combined Chlorine” is a generic chemical term for chemical compounds formed from the reactions of chlorine with organic and biological contaminants in pool water.

Chlorine, and specifically the active chlorine compound hypochlorous acid (HOCl), is a very powerful oxidizer. Oxidizers, in chemical terms, take electrons away from the molecules that they oxidize and, in the process, break those molecules down into different compounds. The most common forms of combined chlorine found in swimming pools are those compounds where chlorine has reacted with nitrogen-containing chemicals in human bather waste (sweat, urine, etc).

CC - Further Reading

www.troublefreepool.com www.troublefreepool.com
Shapshftr said:
And when your CYA is too high, any chlorine above what it can stabilize is inactive, and it makes the test appear to be less than it actually is.
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Not sure what to make of this statement. The cyanuric acid concentration determines the amount of active chlorine (hypochlorous acid + hypochlorite ion) available in pool water. This is why the CYA level is so critical to know and why TFP teaches that there is no such thing as an absolute FC level which is safe; the safe level of FC is determined by how much CYA is in the water.

Pool Water Chemistry

This thread presents my findings so far on pool water chemistry including the following: More Accurate Calcite Saturation Index (CSI) to replace Langelier Saturation Index (LSI) Calculation of ppm HOCl (disinfecting chlorine) at various levels of Total Free Chlorine (FC) and Cyanuric Acid (CYA)...
www.troublefreepool.com www.troublefreepool.com
Shapshftr said:
"The other thing people do is test the water and determine they need to add chlorine. However, every time they test the water, it keeps reading low, no matter how much chlorine they add. This means that your CYA has it locked up."
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Read the pool water chemistry and chlorine lock threads. If that happens, you have let your FC get to low for your CYA and have algae in the pool that consumes the FC. High levels of FC can eradicate the algae. See link-->SLAM Process
Shapshftr said:
The best way to beat it is to partially drain the pool to lower CYA. I know people who have not kept their CYA levels low, and end up with a green pool, over and over again. Then they have to shock the heck out of it, but the problem just keeps returning.
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This is true, reducing CYA makes it easier to SLAM a pool and get rid of algae. They get a green pool at high CYA levels because they did not maintain their FC appropriately for their CYA...follow the recommendations. Link-->FC/CYA Levels
 
I found that the higher the FC the more the testing variance can interfere with OCLT (doing 60 drops vs 28 is harder to get all 60 right)

The advice I was given was that if near end of slam to let high FC drop before doing a OCLT
 
I found that the higher the FC the more the testing variance can interfere with OCLT (doing 60 drops vs 28 is harder to get all 60 right)

The advice I was given was that if near end of slam to let high FC drop before doing a OCLT
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That's correct and I think your strategy to let the FC come down is quite wise
 
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